Field of the Invention
The present invention relates to a method for manufacturing a structure by welding with friction stir welding, and, more particularly, relates to a method for manufacturing a structure by welding an edge portion of the structure formed by stacking a plurality of members with friction stir welding, and to a structure manufactured thereby.
Description of the Related Art
When a plurality of members are stacked and welded, for example, since an aluminum member has a low melting point, it is difficult to apply fusion welding in which a material is melted at high temperature so as to be welded. Hence, in recent years, friction stir welding in which a material is softened without being melted and is welded while being stirred has been widely applied to the welding of a metal having a low melting point metal such as aluminum. In the friction stir welding, a friction stir welding tool is rotated and pressed onto a work in order to supply a necessary amount of heat for the welding. Therefore, a part of a tool tip end surface in the tool called a shoulder is brought into contact with the work during welding, and the contact part of the shoulder and the work after the welding remains having a welding line provided with a width substantially equal to the shoulder diameter. There has been proposed, for example, a cooling plate such as a backing plate for sputtering which is integrally formed by welding with a base portion of a flat-shaped cooling part having therewith a flow path of a coolant.
Although it is preferable to minimize the width of the welding line in the edge portion on the outer circumference of the cooling plate in order to reduce the size of the cooling plate, a width with which the shoulder of the tool makes contact is required in a friction stir welding as described above. Hence, since the edge portion which is friction stir welded on the outer circumference of the cooling plate is equal to or more than the shoulder diameter of the tool, it is difficult to reduce the size of the cooling plate in the production by friction stir welding. In particular, when a plate member on the pressed side of the tool is thick, a tool having a shoulder diameter to perform the friction stir welding and the width of contact by the shoulder of the tool onto the plate member is further increased, with the result that the width of the edge portion of the cooling plate is further increased.